The 802.11u standard corresponds to the standard defined for the purpose of discovering information on an external network connected to an AP (Access Point). Particularly, the 802.11u standard allows a user device to discover network information and a network without a connection with the AP. FIG. 1 illustrates an operation in which the user device discovers a network with an external advertisement server according to a protocol of 802.11u.
Referring to FIG. 1, a user device 10 receives a beacon message broadcasted by an AP 20 in step 51, transmits/receives a probe request and response message to/from the AP 20 in steps 53 and 55, and acquires information indicating provision of advertisement service through the AP 20 in an AP scan process. Thereafter, the user device 10 transmits an advertisement service request message to the AP 20 in step 57 and, accordingly, the AP 20 makes a request for the advertisement service to an advertisement server 30 in step 59. The advertisement server 30 transfers advertisement information to be transmitted to the user device 10 to the AP 20 in response to the request of the AP 20 in step 61. The advertisement information may include information corresponding to each of a plurality of advertisement items. The AP 20 transmits an advertisement service response message including advertisement information to the user device 10 in step 63, and the user device 10 provides a user with the received advertisement information. Thereafter, when a predetermined scan period passes in step 64, the user device 10 repeatedly perform the AP scan process using the probe request and response message in steps 53 and 55, and the advertisement information request process using the advertisement service request and response message in steps 57 to 63.